Conventionally, there is a known variable stroke characteristic engine that includes a variable stroke link mechanism formed from an upper link having one end linked to a piston pin of a piston, a lower link linked to the other end of the upper link and linked to a crankpin of a crankshaft, and a control link having one end linked to the lower link and the other end swingably linked to an engine main body, in which the stroke travel of the piston is made variable by driving the control link by an actuator (ref. Patent Publications 1 and 2).    Patent Publication 1: Japanese Patent Application Laid-open No. 2006-177192    Patent Publication 2: Japanese Patent Application Laid-open No. 9-228858